Optical data discs are an increasingly popular media choice for the distribution and accessing of large volumes of data. This includes audio and video program material, as well as computer programs and data. Formats of optical data discs include audio CD, CDR, CD-ROM, Videodisc and various types of magneto-optical discs. Optical data discs are generally produced by making a master which has physical data features representing the data formed in or on a reference surface therein. The master is used to make a stamper which in turn is used to make production quantities of replica discs, each containing the data which was formed in the master. The high data capacity, convenience and relatively low cost of such discs have contributed to their great success and acceptance in the marketplace. Unfortunately, the high value of the data on a disc, the relative low cost of production of discs, and the proliferation of facilities world wide for mass-production of discs have lead to concerns about counterfeiting of discs.
It would be desirable to have a way of marking discs in a way that would identify a disc as being authentic, that is, as having been manufactured by an authorized source. Ideally, a system of marking would be easy and inexpensive to apply at the authorized disc manufacturing facility, and difficult to duplicate by an unauthorized facility.
The use of special logos or marks on the `label` portion of a disc are not secure from duplication, as most label information is printed using standard graphic arts techniques which are easy to copy and duplicate. Coding of identification in the data on the disc is a possibility, but as `normal` data would be duplicated by the counterfeiter, the identification data would have to be of a non-standard type or location, and this in turn would probably require special playback equipment or analysis to interpret. In other fields, such as credit cards, security has been provided by inclusion of additional layers having magnetic patterns, or inclusion of a hologram layer laminated in the card. However, it would be desirable to provide special logos or marks on optical data discs without having to provide additional layers to do so.